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Iridoid glucosides as sources of cyclopentanoid 1,5-dialdehydes: Conversion of aucubigenin to aucommial and eucommiol
0031-9422/87 s3.00+ 0.00 PcrgamonJournalsLtd.
Vol. 26, No. 5, pp. 1449-1451, 1987. ~by~~~~ry, Printedm Great Britain.
IRIDOID GLUCOSIDES AS SOURCES OF CYCLOPENTANOID 1,5-DIALDEHYDES: CONVERSION OF AUCUBIGENIN TO EUCOMMIAL AND EUCOMMIOL ENRICODAVINI,CARLOIAVARONE* and CORRAD~TROM)LO* Centrodi Studio per la Chimica dclle Sostaoze.Organiche Naturali del CNR, Roma, Italy; l Diprtimcnto di Chimica dell’Universid ‘La sapicnza’. P. Ic Aldo Moro $00185 Roma, Italy (Reukd
received
t July
1986)
Key Word ID&X-Eucommia uinwideq Eucommiacea~aucubin; aucubigenin; iridoid aglywns; euwmmioi: ‘H NMR and “CNMR.
euwmmial,
Abstract-Aucubigenin, which exists only in the closed hemiacetal form, has been transformed into a stable conjugated l,S-dialdehyde form, ‘eucommial’, by a base-catalysed A7 -+ As double-bond shift. Further reduction of eucommial leads to eucommiol, which co-occurs with aucubin in the autumn in Eucommia ulmoides and Aucuba japonica. The successful transformation of aucubin to eucommiol seems to support an in uiuo relationship between these compounds.
acidic [5,6] or enzymatic [7] conditions, leads to the conjugated dialdehyde form 8 of the aglycone. In recent years we isolated from Eucommia ulmoides, Previous attempts to obtain the double-bond shift on 5 besides aucubin (I) and other iridoid glucosides, cycloby mild acid catalysis were unsuccessful because instead of pententetrol(2) [l] (eucommiol) and two of its glucosides, the expected dialdehyde 6, l,lO-anhydro-3,4dihydro-4eucommioside I (3) (2”-O-/I-glucopyranosyleucommiol) decarbomethoxy-3a-hydroxygardenogenin (9) [8,9] was [2] and, more recently, eucommioside III, the structure of isolated. which is now under inv~ti~tion. A third glucoside, The target has now been reached by treating 5 with eucommioside II (4) (1-O-~-glucopyranosyleu~mmiol) anhydrous sodium carbonate in ethyl acetate or acetone was isolated, in addition to 1 and 2, from Aucubajaponica solution at 70’ for 24-48 hr. Compound 6 (named (Cornaceae) [3]. eucommial because of its analogy with 2) was obtained in Compounds 2, 3 and 4 are all present in these plants good yields (7&80x) and exhibits interesting spectral only in the autumn, whereas 1 is present in the plants all features. The ‘HNMR spectrum in CD,COCD, (see the year round and is the most abundant iridoid. These Experimental) fits perfectly with the assigned dialdehyde facts and the structural analogy between 2 and the structure, showing a singlet at 6 10.23 for the conjugated dialdehyde form of au~bi~~n (5) (the aglycone of 1) formyl groupat C3t,and a narrow triplet (J = 1.9 Hz)at seem to indicate that there is a relationship between these 69.74 for the formyl group of the side chain at C-2. By compounds in viuo. We have now verified the possibility of contrast, the ‘H NMR spectrum in D,O shows the converting 1 into 2, via 5, by inducing a double-bond shift contemporaneous presenceat equilibrium of dialdehyde 6 (A’ + A*) in the aglycone and reducing the conjugated and its monohydrate form 10, whereas only the undialdehyde 6. conjugated CHO group is involved in the hydration. An approximate 2:3 ratio can be inferred from the integral 2.5: 1 ratio between the signalsat 69.90 (conjugated CHO) RESULTS and 69.60 (unconjugated CHO). This integral difference is This attempt was made easier by the application of our balanced by the appearance of a triplet (J = 5.5 Hz) at SS.10, partly masked by the HDO signal, which can be recent method, which provides 5 quantitatively (yield > 95 “/ok by continuous extraction with refluxing ethyl clearly assigned to the methine proton of the hydrated formyl group. The other protons give a mixture of acetate of the aqueous mixture obtained upon enzymatic hydrolysis of 1 with fl-glucosidase [4]. overlapping signals from both forms. The equilibrium of aucubigenin (!I) is completely In agreement with the ‘HNMR spectrum, the shifted towards the hernia&al form (the resonance signal “C NMR spectra (PND and SFORD) of 6 in of the formyl proton is absent in its ‘H NMR spectrum in CD,COCD, (see Experimental) show two aldehyde carDzO), as found in al1 iridoid aglycones. The only excep- bons at 6 189.81 (~nju~t~) and 202.24 (u~onju~t~~ tion to this rule is represented by the aglycone of 6,10- respectively, and two conjugated olefinic carbons at 6 163.29 (a C-3) and 139.00 fs Cd), whereas the spectra of bisdeoxyaucubin (7) which, upon hydroiysis under either the same compound in D20 are characterizd by the presence of signals of both anhydrous and hydrated forms at equilibrium. The selective hydration of the unconjugated carbonyl t By analogy with previouspapers [l-3], cyclopcntcqoliols group of eucommial (6) is consistent with the known and derivatives were numbered according to WPAC r&s. INTRODUCTION
1449
Ii. DAVINIet al.
1450 R 4i
, ‘0
<..’ DC
CHaR OGIC 2 R=R'=H 3 R =Glc; R’-H 4 R = H; R' = Glc
R-OH 7 R=H 1
OH
OH
CH,OH B
>>a
R 2’ 1 s 4-
A “CHAR
.a’ 2 3
2” zr:
HO
[HO
6
R=OH 8 R=H 11 R = OAc
10
differences in reactivity of conjugated and unconjugated aldehyde groups in water [lo]. Acetylation of eucommial(6) gave the diacetate 11,the structure of which is consistent with its ‘H NMR and ‘%ZNMR spectra (see Experimental). As expected, sodium borohydride reduction of 6 in aqueous solution gave, in quantitative yields, a cyclopententetrol whose ‘H NMR and 13C NMR data were coincident with those of natural 2. The ready transformation of 1 to 2 supports the initial hypothesis that the Nurrence of these compounds in plants is of biogenetic significance. On the other hand, the fact that the chiral synthons 6 and 2 are easily obtained in good yields is of great interest for the synthesis of natural cyclopentanoid compounds, which we are currently carrying out [ 111.
9
General prtlcedure for the preparation
General techniques have been described earlier [43. ‘H NMR were run at 300 or 90 MHz chemical shifts as 6, coupling constants in Hz, HDO as internal standard at 4.70 ppm for D1O solns and TMS as internal standard for CIXl, and CD,COCDJ solns. 13CNMR spectra were run at 20 MHz; chemical shifts as ppm from TMS, dioxane as internal standard (67.4 ppm from TMS) for D20 solns, TMS as internal standard for CDCI, and CD&OCD,
solns.
(6). h-y
aucubigenin (5) (so0 mg) [47. The soln was stirred at 70” until 5 was completely transformed (ca 24-48 hr), and the reaction was checked by TLC (EtOAc-MeOH, 9: 1). After cooling, the salts were filtered and washed with EtOAc. The combined solns were dried (Na,SO,) and evaporated in uacuo. For analytical purposes, the amorphous residue (400mg) was chromatographed on ‘washed’silica gel with EtOAc-Me2C0 (4: 1)and afforded pure 6 (MO mg). ‘H NMR of 6 (300 MHz, CD,COCD3): 6 10.23 (LH, S, H-3’), 9.74 (lH, t, &+, 2H_2’ = 1.9 Hz, H-2”), 4.65 (2H, br s, ZH4’),4.06 (lH, sext, J1, s = 6.0, J,, 2 = 2.0 Hq H-l), 3.01 (lH, dd, pv-
- 18.0, J,, 5 = 6.0 Hz, H-5), 2.98-2.90
(1 H, complex m, H-
overlapped by signals of H-5 to lower field), 2.64 (1H, act,J,, - 1.9 Hz, H&l, 2.54 (lH, br d, = 18.0 Hz, H-S), 2.41 (IH, act, J,, = 18.0, JH_SA = 9.0,
= 18.0, J,+&a = 6.0, J,_,,, Jks8
EXPERIMENTAL
of eucommial
Na,CO, (5 g)wasadded to an EtOAc or MczCO soln (300 ml) of
I”_,.,, = 1.9 Hq H,2’). lH NMR of 6 + 10 (90 MHz, D20): S9.90 (lH, s, H-Y), 9.60 (IH, t, H-2”), 5.10 (lH, t, CH(OH)r at 2”). 1.70 (ZH, m, CHzCH (OH),). “CNMR of 6 (CD,COCD,): 620224 (d, C-2”), 189.81 (d, C-3’), 163.29 (s, C-3), 139.00 (s, C-4). 74.98 (d, C-L), 59.91 (t, C4’), 49.25 (d, C-2), 45.94 (t, C-S), 44.30 (t, C-2’). 13C NMR of 6+ 10 (D,O): 206.97 (d, C-2”), 192.22 (d, C-3’), 90.64 (d, C-Z”), 38.88 (t, C-2’). Bis-0-acetyleucomtnia1 (11).Compound 6 (100 mg) was dissolved in dry C5HSN (2.5 ml) and AczO (5 ml) and after standing at room temp. for 1 hr, McOH (5 ml) was added at 0”. After
Eucommial and eucommiol from aucubigenin 30 min. the soln was evaporated in vacua, affording a residue which was chromatographed on silica gel (CHCI,-Et,O, 7: 3) to give I1 asanoil(90 mg). ‘H NMR (90 MHz, CDCIJ):6 10.03(lH, s, H-3’),9.68 (lH, 1,H-2”), 5.10(2H,brs,2H4’),4.98 (lH,sext,H-l), 3.43(1H,m,H-2),3.22(1H,dd,H-5),2.80(2H,~2H-2’),2.60(1H, br d, H-5). 2.10and 2.02 (s, AcD). 13C NMR (CDCI,): 6200.21 (d, C-2”). 187.23(d. C-3’), 170.67 (s, AcO), 154.82(s,C-3), 139.82(s, C4), 76.25 (d, C-l), 59.38 (1.C-4’), 46.28 (d, C-2), 44.60 (t, C-5), 41.73 (t, C-2’). 20.99 (q. AcO), 20.64 (q, AcO). Eucommiol (2) by reduction oj 6 with NaBH,. Compound 6 (300 mg) was dissolved in Hz0 (5 ml) and treated with an excess of NaBH, (ca 10 equiv.). After 15 min. the reaction was interrupted by neutralization to pH 7 by bubbling CO1. The soln was adsorbed on decolourizing charcoal (5 g). The suspension, as a layer on a Gooch funnel, was washed with Hz0 to remove the salts, and then eluted with MeOH. The MeOH soln was evaporated in vacua and left a residue (2SOmg) which was chromatographed on cellulose powder with n-BuOH saturated with H20, to give pure 2 (200 mg). ‘H NMR and “C NMR data were in agreement with those reported [2,12]. ‘HNMR (90 MHz, D,O) [2]: 64.24 (5H, br s, H-l, ZH-3’, 2H-4’), 3.71 (ZH, t, J = 7.0 Hz, 2H-2”), 2.90 (lH, br dd, J,, = 18.0 Hz, Ha-S), 2.72 (IH, m, H-2), 2.32 (lH, br d, J,,, = 18.0 Hq H,5), 2.1-1.2 (2H, comp/exm,2H-2’). “CNMR (D,O)f12]:6138.96(s,C-4), 137.11 (s, C-3). 75.30 (d, C-l), 60.84 (1.C-2”). 57.91 (kC4’), 56.17 (1.C-3’). 52.93 (d, C-2). 42.19 (t, C-5), 33.11 (r, C-2’):
Acknowledgement-This
work was supported by the National
1451
Research Council of Italy (CNR) within the Oriented Project ‘Chimica Fine e Secondaria’. REFERENCES 1. Bianco, A., Iavarone, C. and Trogolo, C. (1974) Tetrahedron 30,4117. 2. Bianco, A., Bonini, C., Iavarone, C. and Trogolo. C. (1982) Phytochemis~ry 21, 201. 3. Bernini, R., lavarone, C. and Trogolo, C. (1984) Phytochemistry 23, 1431. 4. Davini, E., lavarone, C., Trogolo, C., Aureli, P. and Pasolini, B. (1986) Phytochemistry 25, 2420. 5. Grimshaw, J. and Juneja, H. R. (1960) Chem. Ind. 656. 6. Birch, A. J. and Subba Rao, G. (1972) in Advances in Orgmic Chemistry (Taylor, E. C., ed.) Vol. 8. p. 39. WileyInterscience, New York. 7. Bianco, A., Guise, M., lavarone, C., Passacantilli, P. and Trogolo, C. (1977) Tetrahedron 33, 851. 8. Bianco, A., Guise. M.. Iavarone, C., Passacantilli, P. and Trogolo. C. (1977) Tetrahedron 33, 847. 9. Bianw, A., Guise, M., lavarone, C., Passacantilh. P. and Trogolo. C. (1984) Tetrahedron 40, 1191. 10. Gould, E. S. (1969) Mechanism and Structure in Organic Chemiswy, p. 540 and refs. cited therein. Holt, Reinehart Winston, London. 11. Davini, E., lavarone, C. and Trogolo, C. (1985) 15th Annual Meeting of the Socied Chimica Italiana, Sirmione. Italy, 22-27 September 1985, Abstracts, p. 481. 12. Bianco. A., Bonini, C., Guise, M., Iavarone, C. and Trogolo, C. (1981) Tetrahedron 37, 1773.
Vol. 26, No. 5, pp. 1449-1451, 1987. ~by~~~~ry, Printedm Great Britain.
IRIDOID GLUCOSIDES AS SOURCES OF CYCLOPENTANOID 1,5-DIALDEHYDES: CONVERSION OF AUCUBIGENIN TO EUCOMMIAL AND EUCOMMIOL ENRICODAVINI,CARLOIAVARONE* and CORRAD~TROM)LO* Centrodi Studio per la Chimica dclle Sostaoze.Organiche Naturali del CNR, Roma, Italy; l Diprtimcnto di Chimica dell’Universid ‘La sapicnza’. P. Ic Aldo Moro $00185 Roma, Italy (Reukd
received
t July
1986)
Key Word ID&X-Eucommia uinwideq Eucommiacea~aucubin; aucubigenin; iridoid aglywns; euwmmioi: ‘H NMR and “CNMR.
euwmmial,
Abstract-Aucubigenin, which exists only in the closed hemiacetal form, has been transformed into a stable conjugated l,S-dialdehyde form, ‘eucommial’, by a base-catalysed A7 -+ As double-bond shift. Further reduction of eucommial leads to eucommiol, which co-occurs with aucubin in the autumn in Eucommia ulmoides and Aucuba japonica. The successful transformation of aucubin to eucommiol seems to support an in uiuo relationship between these compounds.
acidic [5,6] or enzymatic [7] conditions, leads to the conjugated dialdehyde form 8 of the aglycone. In recent years we isolated from Eucommia ulmoides, Previous attempts to obtain the double-bond shift on 5 besides aucubin (I) and other iridoid glucosides, cycloby mild acid catalysis were unsuccessful because instead of pententetrol(2) [l] (eucommiol) and two of its glucosides, the expected dialdehyde 6, l,lO-anhydro-3,4dihydro-4eucommioside I (3) (2”-O-/I-glucopyranosyleucommiol) decarbomethoxy-3a-hydroxygardenogenin (9) [8,9] was [2] and, more recently, eucommioside III, the structure of isolated. which is now under inv~ti~tion. A third glucoside, The target has now been reached by treating 5 with eucommioside II (4) (1-O-~-glucopyranosyleu~mmiol) anhydrous sodium carbonate in ethyl acetate or acetone was isolated, in addition to 1 and 2, from Aucubajaponica solution at 70’ for 24-48 hr. Compound 6 (named (Cornaceae) [3]. eucommial because of its analogy with 2) was obtained in Compounds 2, 3 and 4 are all present in these plants good yields (7&80x) and exhibits interesting spectral only in the autumn, whereas 1 is present in the plants all features. The ‘HNMR spectrum in CD,COCD, (see the year round and is the most abundant iridoid. These Experimental) fits perfectly with the assigned dialdehyde facts and the structural analogy between 2 and the structure, showing a singlet at 6 10.23 for the conjugated dialdehyde form of au~bi~~n (5) (the aglycone of 1) formyl groupat C3t,and a narrow triplet (J = 1.9 Hz)at seem to indicate that there is a relationship between these 69.74 for the formyl group of the side chain at C-2. By compounds in viuo. We have now verified the possibility of contrast, the ‘H NMR spectrum in D,O shows the converting 1 into 2, via 5, by inducing a double-bond shift contemporaneous presenceat equilibrium of dialdehyde 6 (A’ + A*) in the aglycone and reducing the conjugated and its monohydrate form 10, whereas only the undialdehyde 6. conjugated CHO group is involved in the hydration. An approximate 2:3 ratio can be inferred from the integral 2.5: 1 ratio between the signalsat 69.90 (conjugated CHO) RESULTS and 69.60 (unconjugated CHO). This integral difference is This attempt was made easier by the application of our balanced by the appearance of a triplet (J = 5.5 Hz) at SS.10, partly masked by the HDO signal, which can be recent method, which provides 5 quantitatively (yield > 95 “/ok by continuous extraction with refluxing ethyl clearly assigned to the methine proton of the hydrated formyl group. The other protons give a mixture of acetate of the aqueous mixture obtained upon enzymatic hydrolysis of 1 with fl-glucosidase [4]. overlapping signals from both forms. The equilibrium of aucubigenin (!I) is completely In agreement with the ‘HNMR spectrum, the shifted towards the hernia&al form (the resonance signal “C NMR spectra (PND and SFORD) of 6 in of the formyl proton is absent in its ‘H NMR spectrum in CD,COCD, (see Experimental) show two aldehyde carDzO), as found in al1 iridoid aglycones. The only excep- bons at 6 189.81 (~nju~t~) and 202.24 (u~onju~t~~ tion to this rule is represented by the aglycone of 6,10- respectively, and two conjugated olefinic carbons at 6 163.29 (a C-3) and 139.00 fs Cd), whereas the spectra of bisdeoxyaucubin (7) which, upon hydroiysis under either the same compound in D20 are characterizd by the presence of signals of both anhydrous and hydrated forms at equilibrium. The selective hydration of the unconjugated carbonyl t By analogy with previouspapers [l-3], cyclopcntcqoliols group of eucommial (6) is consistent with the known and derivatives were numbered according to WPAC r&s. INTRODUCTION
1449
Ii. DAVINIet al.
1450 R 4i
, ‘0
<..’ DC
CHaR OGIC 2 R=R'=H 3 R =Glc; R’-H 4 R = H; R' = Glc
R-OH 7 R=H 1
OH
OH
CH,OH B
>>a
R 2’ 1 s 4-
A “CHAR
.a’ 2 3
2” zr:
HO
[HO
6
R=OH 8 R=H 11 R = OAc
10
differences in reactivity of conjugated and unconjugated aldehyde groups in water [lo]. Acetylation of eucommial(6) gave the diacetate 11,the structure of which is consistent with its ‘H NMR and ‘%ZNMR spectra (see Experimental). As expected, sodium borohydride reduction of 6 in aqueous solution gave, in quantitative yields, a cyclopententetrol whose ‘H NMR and 13C NMR data were coincident with those of natural 2. The ready transformation of 1 to 2 supports the initial hypothesis that the Nurrence of these compounds in plants is of biogenetic significance. On the other hand, the fact that the chiral synthons 6 and 2 are easily obtained in good yields is of great interest for the synthesis of natural cyclopentanoid compounds, which we are currently carrying out [ 111.
9
General prtlcedure for the preparation
General techniques have been described earlier [43. ‘H NMR were run at 300 or 90 MHz chemical shifts as 6, coupling constants in Hz, HDO as internal standard at 4.70 ppm for D1O solns and TMS as internal standard for CIXl, and CD,COCDJ solns. 13CNMR spectra were run at 20 MHz; chemical shifts as ppm from TMS, dioxane as internal standard (67.4 ppm from TMS) for D20 solns, TMS as internal standard for CDCI, and CD&OCD,
solns.
(6). h-y
aucubigenin (5) (so0 mg) [47. The soln was stirred at 70” until 5 was completely transformed (ca 24-48 hr), and the reaction was checked by TLC (EtOAc-MeOH, 9: 1). After cooling, the salts were filtered and washed with EtOAc. The combined solns were dried (Na,SO,) and evaporated in uacuo. For analytical purposes, the amorphous residue (400mg) was chromatographed on ‘washed’silica gel with EtOAc-Me2C0 (4: 1)and afforded pure 6 (MO mg). ‘H NMR of 6 (300 MHz, CD,COCD3): 6 10.23 (LH, S, H-3’), 9.74 (lH, t, &+, 2H_2’ = 1.9 Hz, H-2”), 4.65 (2H, br s, ZH4’),4.06 (lH, sext, J1, s = 6.0, J,, 2 = 2.0 Hq H-l), 3.01 (lH, dd, pv-
- 18.0, J,, 5 = 6.0 Hz, H-5), 2.98-2.90
(1 H, complex m, H-
overlapped by signals of H-5 to lower field), 2.64 (1H, act,J,, - 1.9 Hz, H&l, 2.54 (lH, br d, = 18.0 Hz, H-S), 2.41 (IH, act, J,, = 18.0, JH_SA = 9.0,
= 18.0, J,+&a = 6.0, J,_,,, Jks8
EXPERIMENTAL
of eucommial
Na,CO, (5 g)wasadded to an EtOAc or MczCO soln (300 ml) of
I”_,.,, = 1.9 Hq H,2’). lH NMR of 6 + 10 (90 MHz, D20): S9.90 (lH, s, H-Y), 9.60 (IH, t, H-2”), 5.10 (lH, t, CH(OH)r at 2”). 1.70 (ZH, m, CHzCH (OH),). “CNMR of 6 (CD,COCD,): 620224 (d, C-2”), 189.81 (d, C-3’), 163.29 (s, C-3), 139.00 (s, C-4). 74.98 (d, C-L), 59.91 (t, C4’), 49.25 (d, C-2), 45.94 (t, C-S), 44.30 (t, C-2’). 13C NMR of 6+ 10 (D,O): 206.97 (d, C-2”), 192.22 (d, C-3’), 90.64 (d, C-Z”), 38.88 (t, C-2’). Bis-0-acetyleucomtnia1 (11).Compound 6 (100 mg) was dissolved in dry C5HSN (2.5 ml) and AczO (5 ml) and after standing at room temp. for 1 hr, McOH (5 ml) was added at 0”. After
Eucommial and eucommiol from aucubigenin 30 min. the soln was evaporated in vacua, affording a residue which was chromatographed on silica gel (CHCI,-Et,O, 7: 3) to give I1 asanoil(90 mg). ‘H NMR (90 MHz, CDCIJ):6 10.03(lH, s, H-3’),9.68 (lH, 1,H-2”), 5.10(2H,brs,2H4’),4.98 (lH,sext,H-l), 3.43(1H,m,H-2),3.22(1H,dd,H-5),2.80(2H,~2H-2’),2.60(1H, br d, H-5). 2.10and 2.02 (s, AcD). 13C NMR (CDCI,): 6200.21 (d, C-2”). 187.23(d. C-3’), 170.67 (s, AcO), 154.82(s,C-3), 139.82(s, C4), 76.25 (d, C-l), 59.38 (1.C-4’), 46.28 (d, C-2), 44.60 (t, C-5), 41.73 (t, C-2’). 20.99 (q. AcO), 20.64 (q, AcO). Eucommiol (2) by reduction oj 6 with NaBH,. Compound 6 (300 mg) was dissolved in Hz0 (5 ml) and treated with an excess of NaBH, (ca 10 equiv.). After 15 min. the reaction was interrupted by neutralization to pH 7 by bubbling CO1. The soln was adsorbed on decolourizing charcoal (5 g). The suspension, as a layer on a Gooch funnel, was washed with Hz0 to remove the salts, and then eluted with MeOH. The MeOH soln was evaporated in vacua and left a residue (2SOmg) which was chromatographed on cellulose powder with n-BuOH saturated with H20, to give pure 2 (200 mg). ‘H NMR and “C NMR data were in agreement with those reported [2,12]. ‘HNMR (90 MHz, D,O) [2]: 64.24 (5H, br s, H-l, ZH-3’, 2H-4’), 3.71 (ZH, t, J = 7.0 Hz, 2H-2”), 2.90 (lH, br dd, J,, = 18.0 Hz, Ha-S), 2.72 (IH, m, H-2), 2.32 (lH, br d, J,,, = 18.0 Hq H,5), 2.1-1.2 (2H, comp/exm,2H-2’). “CNMR (D,O)f12]:6138.96(s,C-4), 137.11 (s, C-3). 75.30 (d, C-l), 60.84 (1.C-2”). 57.91 (kC4’), 56.17 (1.C-3’). 52.93 (d, C-2). 42.19 (t, C-5), 33.11 (r, C-2’):
Acknowledgement-This
work was supported by the National
1451
Research Council of Italy (CNR) within the Oriented Project ‘Chimica Fine e Secondaria’. REFERENCES 1. Bianco, A., Iavarone, C. and Trogolo, C. (1974) Tetrahedron 30,4117. 2. Bianco, A., Bonini, C., Iavarone, C. and Trogolo. C. (1982) Phytochemis~ry 21, 201. 3. Bernini, R., lavarone, C. and Trogolo, C. (1984) Phytochemistry 23, 1431. 4. Davini, E., lavarone, C., Trogolo, C., Aureli, P. and Pasolini, B. (1986) Phytochemistry 25, 2420. 5. Grimshaw, J. and Juneja, H. R. (1960) Chem. Ind. 656. 6. Birch, A. J. and Subba Rao, G. (1972) in Advances in Orgmic Chemistry (Taylor, E. C., ed.) Vol. 8. p. 39. WileyInterscience, New York. 7. Bianco, A., Guise, M., lavarone, C., Passacantilli, P. and Trogolo, C. (1977) Tetrahedron 33, 851. 8. Bianco, A., Guise. M.. Iavarone, C., Passacantilli, P. and Trogolo. C. (1977) Tetrahedron 33, 847. 9. Bianw, A., Guise, M., lavarone, C., Passacantilh. P. and Trogolo. C. (1984) Tetrahedron 40, 1191. 10. Gould, E. S. (1969) Mechanism and Structure in Organic Chemiswy, p. 540 and refs. cited therein. Holt, Reinehart Winston, London. 11. Davini, E., lavarone, C. and Trogolo, C. (1985) 15th Annual Meeting of the Socied Chimica Italiana, Sirmione. Italy, 22-27 September 1985, Abstracts, p. 481. 12. Bianco. A., Bonini, C., Guise, M., Iavarone, C. and Trogolo, C. (1981) Tetrahedron 37, 1773.